Frost weighing demand defrost device for refrigerators



C. D, ESCI-IE FROST WEIGHING DEMAND DEFROST DEVICE FOR REFRIGERATORSFiled May 2, 1969 2 Sheets-Sheet l awww.

Inf/eric?? C. D. ESCI-IE Dec. l5, 1970 FROST WEIGHING DEMAND DEFROSTDEVICE FOR REFRIGERATORS Filed May 2, 1969 2 Sheets-Sheet 2 UnitedStates Patent Oqce 3,546,894 Patented Dec. 15, 1970 3,546,894 FROSTWEIGHING DEMAND DEFROS'I DEVICE FOR REFRIGERATORS Charles D. Esche,Newburgh, Ind., assignor to Whirlpool Corporation, a corporation ofDelaware Filed May 2, 1969, Ser. No. 821,322 Int. Cl. F25d 21/02 U.S.Cl. 62-140 13 Claims ABSTRACT OF THE DISCLOSURE Apparatus for initiatinga -defrost operation of a refrigeration system having an evaporator andmeans for defrosting the evaporator. The apparatus includes a frostcollector arranged to be disposed adjacent the evaporator for collectionof frost thereon concurrently with deposition of frost on theevaporator. A control mechanism is associated with the frost collectorto initiate operation of the defrosting means as a result of acollection of frost on the collector having a preselected weight. Themechanism is arranged to periodically sense the weight of the collectedfrost. Means are provided for adjusting the mechanism to effectinitiation of the defrost operation upon the Weight reaching any one ofa plurality of preselected weights. The mechanism further includes meansfor adjusting the duration of the defrost operation.

BACKGROUND lOF THE INVENTION Field of the invention This inventionrelates to refrigeration systems and in particular to apparatus forcontrolling defrost operatlons in refrigeration systems.

Description of the prior art A large number of different devices andapparatus have been developed for sensing the need for and initiatingdefrosting operations in refrigeration apparatus. In one form ofconventional refrigeration apparatus an evaporator provides heatexchange with the air to be cooled. Frost is deposited on the evaporatoras a result of the cooling of the air, and the collection of such frostpresents a serious problem in the operation of the refrigeratorapparatus as it tends to block free air flow through the evaporator anddecrease efficiency of operation. The amount of frost collected varieswith the humidity and temperature conditions of the air being cooled.Thus it is desirable to provide a control means which is responsive tothe amount of frost actually deposited on the evaporator. However, suchsystems are relatively complex and costly and resort is conventionallyhad to control mechanisms which defrost the evaporator at fixed timeintervals. Such iixed interval defrosting, however, has the disadvantageof inefficiency as the defrosting is effected at times when not requiredsuch as when the air to be cooled is relatively dry cool air. On theother hand there are times when the defrosting operation of the meansfor defrosting the evaporator to defrost time intervals as when the airto be cooled is relatively hot humid air.

SUMMARY OF THE INVENTION The present invention comprehends an improvedapparatus for controlling a defrost operation in a refrigeration systemeliminating the disadvantages of the above discussed defrost controls ina novel and simple manner. More specifically, the invention comprehendsan improved apparatus for initiating a defrost operation of arefrigeration system having an evaporator and means for defrosting theevaporator, the apparatus comprising a frost collection element, meansfor supporting the elementin juxtaposition to the evaporator to havefrost collected thereon concurrently with collection of frost on theevaporator, and means responsive to an increase in the weight of theelement and frost collected thereon for initiating operation of themeans for defrosting the evaporator to defrost the evaporator and saidelement.

Still more specifically the invention comprehends the provision of suchan apparatus having means for causing the sensing of the weight to beperiodical.

Still more specifically, the invention comprehends the provision of suchan apparatus having means for adjusting the operation thereof toinitiate the defrost operation as a function of any one of a pluralityof different preselected combined weights of the collection element andcollected frost.

Still further more specifically the invention comprehends the provisionof such apparatus having means for adjustably controlling the durationof the `defrosting operation.

The invention also comprehends the provision in such apparatus of acontrol mechanism including a lever, means for pivotally mounting thelever, a carrier, means for pivotally mounting the carrier adjacent thelever, means for resiliently biasing the lever and carrier to pivot thelever relative to the carrier, means on the lever for collecting frostand tending to pivot the lever in opposition to the biasing means, andswitch means carried by the carrier to be actuated as a result of apreselective pivoting of the lever resulting from a preselectedcollection of frost on the collecting means.

Still further, the invention comprehends the provision of such a controlmechanism having improved means for adjusting the operation thereof.

BRIEF DESCRIPTION OF THE DRAWING Other features and advantages of theinvention will be apparent from the following description taken inconnecytion with the accompanying drawing wherein:

FIG. 1 is a fragmentary side elevation of an apparatus for initiating adefrost operation in a refrigeration system embodying the invention;

FIG. 2 is a fragmentary side elevation illustrating arrangement of thecontrol mechanism as upon the initiation of a defrost operation;

FIG. 3 is a fragmentary left end view thereof;

FIG. 4 is a fragmentary top plan view thereof;

FIG. 5 is a schematic diagram of the electrical wiring of therefrigeration system;

IG. 6 is a perspective view of the control mechanism; an

FIG. 7 is a front view of a refrigerator-freezer provided with thecontrol mechanism.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the exemplary embodiment ofthe invention as shown in the drawing, a refrigeration system generallydesignated 10 is shown to include a control mechanism 11 which isresponsive to a frost condition in an evaporator 12 to initiateautomatically a defrosting operation thereof. The evaporator maycomprise a conventional evaporator, one form of such evaporatorstructure being illustrated in FIG. 7 wherein the evaporator 12 isdisposed rearwardly of a false rear wall 44 at the rear of the freezercompartment 45 of a conventional refrigerator-freezer apparatus 46. Asshown, the control mechanism 11 may be secured to the cabinet 47 to Ibedisposed superjacent the evaporator.

As discussed briey above, the control mechanism functions as a demanddefrost device in that it effects an initiation of the defrost operationupon a frost build-up in the evaporator to a preselected point. As shownin FIG. 1,

the control mechanism 11 includes a collection element 13 which isdisposed within a space 14 between the ns 15 of the evaporator 12, so asto have frost collect thereon in correspondence to the frost collectionon the ns 15. 'Control mechanism 11 is arranged to sense periodicallythe combined weight of the element 13 and the frost collected thereon,and to initiate the defrost operation when this weight reaches apreselected weight corresponding to a defrost condition of theevaporator requiring such defrosting.

Referring briefly to FIG. 5, the refrigeration system 10 includes acompressor motor 16 connected in series with a conventional relay 17 andstarting capacitor 18 to the power supply lead L-l. The compressor motoris further connected through an overload device 19, a conventionalthermostat switch 20, and a defrost control switch 21 to the other powersupply lead L-2. A defrost heater 22 is connected through an overloaddevice 23 between power supply lead L-1 and the switch 21. Morespecically, switch 21 comprises a single pole, double-throw switchhaving moving contact 21a connected to power supply lead L-2, a fixedContact 21b connected to the overload device 23, and a second fixedcontact 21C connected to the thermostat switch 20. A timer motor 24 isconnected between power supply leads L-1 and L-2 for continuousenergization. Thus, in normal operation, the compressor motor 16 isenergized when the thermostat switch 20 closes as a result of a hightemperature in the space wherein the switch is disposed. The controlswitch 21 is normally disposed, as shown in FIG. 5, with the movingcontact 21a contacting xed contact 21C to complete the circuit to powersupply lead I.-2. At this time, the defrost heater 22 is not energized.

Control mechanism 11 is arranged to effect operation of defrost heater22, as discussed above, as a result of the increase in the weight of thecollected frost on element 13. More specifically, as shown in FIGS. 1through 4 and 6, control mechanism 11 includes a lever 25 which is pivotally mounted to a frame 26 by a pivot pin 27. A double element carrier'28 is similarly pivotally mounted on the frame 26 by the pivot pin 27to extend adjacent the lever 25. The timer motor 24 is mounted on theframe 26 and drives a generally circular cam 29. As shown in FIG. l, thelever extends past cam 29 to overlie evaporator space 14, and collectionelement 13 is hung from the distal end 30 of the lever 25 by a hanger31.

The lever 25 is biased in a counterclockwise direction as seen in FIG. 1and the carrier 28 is biased in a clockwise direction as seen therein bya spring 32 having a coil portion 32a wrapped about pin 27, a first endportion 32h engaging the lever 25, and a second end portion 32e`connected to the carrier 28 through an adjusting screw 33. The adjustingscrew may be locked in an adjusted position by a suitable nut 34 so asto permit ixed adjustment of the spring biasing action tending to urgelever 2'5 and carrier 28 angularly apart on pivot pin 27. As shown inFIG. 1, switch 21 is carried `on carrier 28 to have its actuator 35disposed closely subjaeent lever 25 to be actuated thereby as a resultof a clockwise movement of the lever 25. The clockwise movement of thelever 25 is limited by an adjustable stop screw 36 carried on a bracket37 on frame 26 to be disposed closely subjacent the lever 25.

Lever 25 is provided inwardly of end 30, with a longitudinally slot 38adapted to receive a pointed projection 39 on the cam 29. A pin 40 iscarried on cam 29 to engage periodically a turned portion 41 at the endof carrier 28.

A stop `bracket 42 is mounted on frame 26 subjacent the carrier 21S tolimit the downward, or clockwise, pivoting thereof.

The operation on control mechanism 11 is extremely simple while yetproviding the above described highly desirable control of the frostingoperation. As indicated above, timer motor 24 operates continuously todrive came 29 in a counterclockwise direction as seen in FIG. l.Periodically, i.e., once during each revolution of cam 29, theprojection 39 bears against the underside of lever 25 and pivotallyraises the lever about pivot 27 to raise the collection element 13 andfrost collected thereon relative to space 14. Pin 40 engages the end -41of the carrier 28 to lift the carrier substantially concurrently withthe lifting of lever 25.

As the counterclockwise rotation of the cam 29 continues, projection 39enters slot 38 of the lever 25 permitting the lever to pivot downwardlyagainst the biasing force of spring 32 as the result of the total weightof the element 13 and the frost collected thereon. As thecarrier 28 isnow supported by the pin y40, the lever moves downwardly toward thecarrier. If the total weight of the collected frost and the element 13are suicient to swing the lever 25 against the biasing action of springl32 to cause the lever to engage actuator 35 of switch 21, the movingcontact 21a is thrown from fixed contact 210 to xed contact 21b therebydisconnecting the compressor motor 16 and connecting the defrost heater22 between power supply leads L-1 and L-Z, to initiate the defrostingoperation. If, however, the total weight of element 13 and the frostcollected thereon is insuflicient to pivot the lever 25 against thebiasing action of spring 32 sufficiently to engage actuator 35, switch21 remains as shown in FIG. 5 and no defrosting operation is initiatedduring this cycle of the cam 29. As the cam 29 continues itscounterclockwise rotation, pin 40 moves sufiiciently downwardly topermit the carrier 28 to pivot downwardly and engage the limit stop 42.At the same time, the lever 25 is permitted to pivot downwardly until itengages the adjustable limit stop screw 36 thereby increasing theangular displacement between the carrier and lever. The carrier andlever will remain in the downward position against stops 42 and 36respectively, until the cam once again brings pin y40 and projection 39upwardly to engage the carrier 28 and levers 25 as discussed aboverelative to the previous cycle. The sensing of the weight of element 13and collected frost is again conducted as discussed above and a defrostoperation initiated or the control allowed to further cycle in a manneras discussed above depending on the total weight of the element andcollected frost.

The weight of frost necessary to effect an initiation of v defrostingoperation is controlled by the adjustable screw 33 which provides avariable biasing between the lever 25 and carrier 28. More specifically,spring end 32C may be xed to a washer 43 through which the screw 33passes. Thus, as the screw is threaded into the carrier, the washer 43is urged to the right, as seen in FIG. 1, thereby increasing the forcebiasing the lever 25 upwardly and thereby increasing the weight of froston element 13 necessary to initiate the defrost operation. A reversethreading of screw 33 effects an opposite control of the preselectedweight, i.e., it permits a decrease in the weight necessary to effectthe defrost initiation.

Adjustable stop 36 provides a further highly desirable feature incontrol 11 in permitting an adjustment of the period of the defrostoperation. By adjusting screw 36 to its maximum upward disposition, asshown in FIG. 1, a minimum defrost operation time is obtained as the pin40 permits the carrier 28 to move downwardly from the lever 25 at anearlier point of time. By adjusting the screw 36 downwardly, the lever25 is permitted to move further in a clockwise direction assuming thatsuicient weight of frost on element 13 is present to overcome thebiasing force of spring 32. Thus, carrier 28 must move downwardly agreater distance to terminate the defrost operation as the switch 21must move further downwardly to disengage actuator 35 vfrom the now moredownwardly disposed lever 25.

During a defrost operation, the frost on element 13 will melt and theweight tending to bias the lever 25 downwardly may decrease to belowthat necessary to maintain the lever 25 in actuating relationship toswitch actuator 35. When this occurs the defrost operation is terminatedby opening of switch 21, i.e., the throwing of moving contact 21a fromfixed contact 2lb to fixed contact 21e. If the weight of the frost onelement 13 is not decreased to the point where the lever 25 is spacedfrom actuator to terminate the defrost operation as a result of thedefrosting of element 13, the defrost operation is terminatedautomatically by the movement of the pin suficiently to permit both thelever 25 and carrier 28 to pivot downwardly, i.e., in a clockwisedirection, to engage the lever 25 with the stop screw 36 whilepermitting the carrier to continue to move downwardly to stop 42 andthereby carry the switch away from the lever. Thus, control 11 providesselective termination of the defrost operation either by a sulicientremoval of frost from collection element 13, or lby a maximum time ofdefrost as controlled by cam 29. It should be noted that the sensing ofthe weight of frost on element 13 is periodically effected incontradistinction to those devices wherein the slow build-up of frost ona sensing element gradually causes the movement of a sensing means toeffect a control operation at the instant a preselected weight isreached. In such gradual control devices, the refrigeration system maybe over-sensitive in that any vibration as in closing of therefrigerator door or any slight shock forces may initiate the defrostoperation at times when the total weight is not yet the preselectedWeight. In the control 11, on the other hand, sensing of the weight ofthe collected -frost on the element 13 is effected periodically so thatduring a major portion of time, vibrations and shocks imparted to therefrigeration system ha-ve no effect on the operation of the control.While the Weight of element 13 is a part of the total weight sensed lbythe control mechanism 11, the element weight remains constant at alltimes and, thus, may be cancelled out by suitable selection of thespring parameters. Thus, control mechanism 11 provides substantialimprovement in operation over conventional frost sensing devices Iwhichsense the total weight of the evaporator, as such a system provides a-variable weight in the evaporator corresponding to the amount ofrefrigerant present therein at any given time.

The use of lever 25 and carrier 28 permits the application of suitablemechanical advantages in control mechanism 11 for improved sensitivity.Further, by virtue of the adjustable screw 33, variations in theparameters of spring 32 may be cancelled out by the refrigeratormanufacturer so as to permit the accurate preselection of the frostWeight necessary to initiate operation of the defrosting cycle.

Having described my invention as related to the ernbodiment shown in theaccompanying drawings, it is my intention that the invention be notlimited by any of the details of description, unless otherwisespecified, but rather, be construed broadly within its spirit and scopeas set out in the accompanying claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. Apparatus for initiating a defrost operation of a refrigerationsystem having an evaporator and means for defrosting the evaporator,said apparatus comprising:

a frost collection element;

means for supporting said element in juxtaposition to said evaporator tohave frost collected thereon concurrently with collection of frost onthe evaporator; and

means responsive to an increase in the Weight of said element and frostcollected thereon to a preselected weight for initiating operation ofthe means for defrosting the evaporation to defrost the evaporator andsaid element.

2. The refrigeration system apparatus of claim 1 wherein said last namedmeans includes means for sensing said weight periodically and precludinginitiation of 6 operation of the means for defrosting the evaporator atall other times.

3. The refrigerationl system apparatus of claim 1 wherein saidsupporting means comprises a lever mechanism and last named meanscomprises a switch means actuated by a preselected movement of saidlever mechanism.

4. The refrigeration system apparatus of claim 1 wherein said supportingmeans includes a cam means for cyclically deactivating said last namedmeans for permitting initiation of operation of the means for defrostingthe evaporator only periodically.

5. The refrigeration system apparatus of claim 1 further including meansfor adjusting said apparatus to effect initiation of operation of themeans for defrosting the evaporator at any one of a plurality ofdifferent preselected weights.

6. The refrigeration system apparatus of claim 1 further including meansfor adjustably controlling the duration of operation of the means fordefrosting the evaporator.

7. The refrigeration system apparatus of claim 1 further including meansfor terminating the operation of the means for defrosting the evaporatorafter a preselected time subsequent to the initiation of operationthereof.

8. The refrigeration system apparatus of claim 1 further including meansfor terminating operation of the means for defrosting the evaporatorwhen the weight of said element and frost thereon decreases to apreselected weight as a result of removal of frost from said element inthe defrosting operation.

9. The refrigeration system apparatus of claim 1 further including meansfor periodically sensing the weight of said element and frost thereonafter initiation of the operation of the means for defrosting theevaporator to terminate operation `when the weight of said element andfrost thereon decreases to a preselected Weight as a result of removalof frost from said element in the defrosting operation.

10. Control mechanism comprising:

a lever; means for pivotally mounting said lever;

a carrier; means for pivotally mounting said carrier subjacent saidlever;

means for resiliently biasing said lever and carrier to pivot said leverrelative to said carrier; means on said lever for collecting frost andtending to pivot said lever in opposition to said biasing means;

and switch means carried by said carrier to be actuated as a result of apreselection pivoting of said lever resulting from a preselectedcollection of frost on said collecting means.

11. The control mechanism of claim 10 further including means supportingthe lever against the Weight of said collecting means and frost, andmeans periodically vitiating said supporting means to pivot the weightto urge the lever to actuate said switch means.

12. The control mechanism of claim 11 wherein said vitiating meanscomprises an adjustable screw.

13. The control mechanism of claim 11 including means for adjusting thebiasing force of said means for resiliently biasing said lever andcarrier.

References Cited UNITED STATES PATENTS 1,815,383 7/1931 Scullen 62--1392,511,419 6/1950 Smith 62--140 3,229,474 l/ 1966 Wilson 62-140 MEYERPERLIN, Primary Examiner U.S. Cl. XR. 62-l5l, 157

